There is a small problem with the tree pane in XnView 1.90.3 and 1.91 (on Windows 2000).
When you use cursor keys to select a folder in the tree pane, XnView loads the selected folder twice. It starts loading the thumbnails, but then, after a few milliseconds, it clears the thumbnail pane and starts loading the same folder again.
It doesn't happend when you click the folder.